In 2013, this was true for the vast majority of the U.S. To analyze this, I paired stations in the GHCN v.3 database with 1981-2010 daily normal values published by NCDC. For the Lower 48, I only used primary stations (n=866) and for Alaska I used both primary and Cooperative stations (n=103). In each case there had to be no more than 25% of days with missing or flagged data.
On the maps, anything shaded in blue indicates that less than 4.6% of days were more than 2 standard deviations from the daily mean. Yellow, orange, and red colors show areas that exceeded the expected rate of days that were more than +2 standard deviations or less than -2 standard deviations from the daily normal.Only a few areas in the Intermountain West and much of Alaska had significantly more than 5% of days greater than 2 standard deviations from the daily mean.
The 'Winner' for primary (USW) stations in the entire U.S. was Anchorage's Merrill Field with a value of 10.1%. The Delta 6N Cooperative station in Alaska actually had a value of 11.9%. Figure 3 shows the stations with the largest percentage of +/- 2 standard deviation days.
Figure 2. Percentage of days in the U.S. more than +2 standard deviations or less than -2 standard deviations from the daily normal.
Figure 3. List of stations ranked my the highest number of percentage of days more than +2 standard deviation or less than -2 standard deviations from the daily normal.